The present invention relates to a liquid cooling system for cooling at body that is generating heat, and, in particular, to a liquid cooling system that is suitable for use in a small and/or thin electronic device.
Semiconductor devices that are used in electronic devices, such as a computer, etc., generate heat during their operation. In particular, high-integrated semiconductor devices, in recent years, have produced an increased amount of heat generation. Since the semiconductor device will be damaged if the temperature thereof exceeds a certain value, cooling is necessary to prevent damage to the semiconductor device having a large amount of heat generation during use.
For cooling the semiconductor device of an electronic apparatus, there are various known techniques, such as thermal conduction or air-cooling, or the use of a heat pipe, or liquid cooling.
Cooling by thermal conduction can be achieved by using materials having a large thermal conductivity along the heat radiation route, extending from the semiconductor device to the outside of the electronic apparatus. This method has been suitable for a so-called compact electronic apparatus, in which heat generation is relatively small, such as a notebook-type personal computer.
With cooling by the use of forced air, an air blower or fan is provided inside the electronic apparatus, thereby achieving a cooling of the semiconductor device therein by forced circulation of air thereon. This method is adopted widely for the cooling of semiconductor devices having a higher amount of heat generation, and it also has been applied to a personal computer by making the air blower small and thin in size.
Cooling with the use of a heat pipe, involves carrying heat out the outside of the electronic apparatus by means of coolant enclosed within a pipe, as described in Japanese Patent Laying-Open No. Hei 1-184699 (1989), and Japanese Patent Laying-Open No. Hei 2-244748 (1989), for example. With this method, since there is no part capable of consuming electric power therein, such as an air blower or fan, such a cooling device has good efficiency, i.e., it increases the cooling through thermal conduction. However, with this method, there is a limit to the amount of heat that can be transferred.
Cooling by means of a liquid coolant is suitable for the cooling of a semiconductor device which generates a large amount of heat, and such a cooling device is described, for example, in Japanese Patent Laying-Open No. Hei 5-1335454 (1993), Japanese Patent Laying-Open No. Hei 6-97338 (1994), Japanese Patent Laying-Open No. Hei 6-125188 (1994), and Japanese Patent Laying-Open No. Hei 10-213370 (1998). However, such a cooling system using a liquid coolant has been restricted as to its field of utilization, such as to a large-scale computer. This is because the cooling system using a liquid coolant requires a large number of parts, such as a pump, a pipe system, heat radiation fins, etc., which are used exclusively for cooling, and so the apparatus comes to be large in size. Thus, it is difficult to maintain a satisfactory reliability when using liquid for cooling compared to other methods. It is also one of the reasons why, on the commercial market, no semiconductor device requiring such a high level of cooling employs a liquid cooling system, other than in the field of large-scale computers.
A technique for adapting liquid cooling to a small-sized apparatus, including a notebook-sized personal computer, is described in Japanese Patent Laying-Open No. Hei 6-266474 (1994). In this cooling device, a header attached onto the semiconductor device and a heat radiation pipe separately located from it are connected with each other by means of a flexible tube to form a cooling system, wherein heat is transferred through the liquid coolant flowing therein, thereby cooling the semiconductor device.
However, there has been a remarkable increase in the heat generation produced from semiconductor devices which are used in electronic devices, such as a personal computer, a server computer, a work station, etc., in recent years, with the result that adoption of such conventional technique for cooling is no longer sufficient in connection with electronic apparatuses that are required to be small and thin in size, in particular, such as a notebook-type personal computer.
An object of the present invention, therefore, is to provide a liquid cooling system that is able to efficiently cool down a heat generating body in which high heat is generated, such as a semiconductor device or element of the type which is used in an electronic apparatus that is small and thin in size, and also to provide a personal computer equipped with such a cooling system.
The object, as mentioned above, according to the present invention, is accomplished by the provision of a liquid cooling system of superior efficiency, which is small and thin in size, or by a personal computer equipped with such a liquid cooling system, being peculiar to the personal computer, which is small and thin in the size thereof.
A pump is necessary for circulation of liquid in a liquid cooling system; however, with a pump of rotational type, which is typically used, it is impossible to realize, in particular, a personal computer that is ultra-small and thin, and has a low electric power consumption, as well. For this reason, it is more effective to use a pump which operates by pressurizing the liquid coolant through reciprocal movement of a member. However, even when using such a pump of the reciprocal type, it is necessary to satisfy certain conditions for the purpose of achieving a system of low electric power consumption, while enabling cooling effectively, as will be described below.
In more detail, according to the present invention, there is provided a liquid cooling system, comprising: a pulsation-type pump for supplying cooling liquid; a heat receiving jacket supplied with said cooling liquid and positioned to receive heat generated from a heat generating body; a heat radiation pipe for radiating heat which is supplied by the cooling liquid passing through said heat receiving jacket; and a passage for circulating the cooling liquid passing through said heat radiation pipe into said pump, wherein said cooling liquid circulates within a closed flow passage. In this cooling system, xcex94Vs is equal to or greater than xcex94Vp, assuming that the inner volume change when said pump emits a pulsation is represented by xcex94Vp, the pressure accompanying said volume change is represented by P, and the volume change due to said pressure P in the flow passage of the cooling liquid, other than in a portion of said pump, is represented by xcex94vs.
Further, for example, said pump emits a pulsation by the reciprocal movement of a member within the pump, and the reciprocal movement of the member in said pump is caused by bending or flexure of a diaphragm. This diaphragm itself, or a driving source of the diaphragm, is preferably formed with a piezo element, from the viewpoint achieving a of small-size, low electric power consumption and low noise, etc. With this, it is possible to maintain a substantial amount of cooling liquid in the system, even in a computer that is small and thin in size, thereby to obtain effective cooling.
Also, a rubber pipe or a resin pipe may be used as at least a portion of the connector pipe which forms the flow passage for carrying said cooling liquid therein, and the surface of said resin or rubber pipe is coated with a metal film or a resin sheet covered with a metal film, thereby suppressing diffusion of the cooling liquid through the rubber and the resin into the atmosphere and enabling conduction of heat with efficiency, as well.
The liquid cooling system defined above, preferably, further comprises an accumulator, in which the volume change of the cooling liquid therein due to said pressure P is equal to or greater than xcex94Vp, from a viewpoint of management of the pressure.
Further, the accumulator has a structure such that it retains the cooling liquid therein and is able to vary the amount of fluid it retains. For example, it may be one that varies the retained amount by self deformation. Or, alternatively, it may have a structure such that it holds a gas within a chamber thereof.
The accumulator mentioned above may be made of a flexible material, such as rubber or resin, for example, thereby being movable in response to a change in pressure. Or, it may be constructed by the use of metal bellows. Or, it may employ a piston mechanism therein.
Further, in the liquid cooling system as described above, it is preferable that said cooling liquid is pressurized at a pressure that is equal to or higher than that of the atmosphere.
Also, in the liquid cooling system as described above, the accumulator has a housing with a supply opening through which said circulating cooling liquid is received and a discharge opening for discharging said cooling liquid therethrough, and a chamber that maintains gas and said cooling liquid therein. It is preferable for said accumulator to be disposed in series with the heat receiving jacket or/and the heat radiation pipe in the circuit of the cooling system.
Further, in a personal computer having such a liquid cooling system, according to the present invention, there is a semiconductor element; a signal input portion; a display device; and a liquid cooling system, including a pulsation-type pump for supplying cooling liquid, a heat receiving jacket supplied with said cooling liquid and positioned to receive heat generated within said semiconductor element, a heat radiation pipe for radiating heat which is supplied by the cooling liquid passing through said heat receiving jacket, and a passage for circulating the cooling liquid passing through said heat radiation pipe into said pump, wherein said cooling liquid circulates with in a closed flow passage. In the liquid cooling system, xcex94Vs is equal to or greater than xcex94Vp, assuming that the inner volume change when said pump emits a pulsation therefrom is represented by xcex94Vp, the pressure accompanying said volume change is represented by P, and the volume change due to said pressure P, in the flow passage of the cooling liquid, other than in a portion of said pump, is represented by xcex94vs.
Furthermore, in a notebook-type personal computer, there is provided a main body, including a semiconductor element and a signal input portion; a display device, having a display portion connected with said main body through a movable mechanism; and a liquid cooling system including a pulsation-type pump for supplying cooling liquid, a heat receiving jacket disposed within said main body and supplied with said cooling liquid and positioned to receive heat generated within said semiconductor element, a heat radiation pipe disposed on a back surface of said display portion of said display device for radiating heat which is supplied by the cooling liquid passing through said heat receiving jacket, and a passage for circulating the cooling liquid passing through said heat radiation pipe into said pump, wherein said cooling liquid circulates within a closed flow passage. The cooling liquid system further includes an accumulator which has a supply opening for supplying said circulating cooling liquid therethrough, and a discharge opening for discharging said cooling liquid therethrough, and the accumulator maintains gas and said cooling liquid therein, wherein amount of the cooling liquid maintained within said accumulator varies in response to emission of a pulsation from said pump.
Moreover, in a detailed embodiment according to the present invention, there is provided a personal computer including a semiconductor element; a signal input portion; a display device; and a liquid cooling system, including an emission pump for supplying cooling liquid in the form of a pulsation by using the reciprocating movement of a diaphragm having a piezo element, a heat receiving jacket supplied with said cooling liquid and positioned to receive heat generated within said semiconductor element, a heat radiation pipe for radiating heat which is supplied by the cooling liquid passing through said heat receiving jacket; an accumulator having a housing with a supply opening for supplying said circulating cooling liquid therethrough and a discharge opening for discharging said cooling liquid therethrough, and a chamber for maintaining gas and said cooling liquid therein, and a passage for circulating the cooling liquid passing through said heat radiation pipe into said pump, wherein said cooling liquid circulates within a closed flow passage, and the amount of the cooling liquid maintained within said accumulator varies in response to emission of a pulsation from said pump.
Next, an explanation will be given of the concept of the present invention with reference to FIGS. 13 to 15. The flow passage in the liquid cooling system according to the present invention is shown diagrammatically in the FIG. 13. The flow passage is constructed with a pump 1 and connector pipes 3, and is filled up with a cooling liquid. The connector pipe 3 is connected to both an outlet and an inlet of the pump, thereby forming a closed loop. The pump 1 is constructed with a housing having a diaphragm 8 mounted for reciprocal movement therein and check valves 9a and 9b. Now, considering a case where the diaphragm is moved from the dashed time position to the position of the solid line, since the cooling liquid within the pump housing is pressurized, the check valve 9b is opened. Repeating this operation continuously, causes a fluid pulse to be emitted periodically from the pump, causing the cooling liquid to circulate along the route thereof. In this instance, for the cooling liquid to move in the direction of the arrows, with the check valve 9a closed, it is necessary for a portion or the entire connector pipe 3 to expand, so that the cooling liquid within the pump is able to flow in that direction.
FIG. 14 shows a relationship between the flow rate Q of the pump and the pressure P. Herein, Pmax indicates the maximum pressure that is generated or developed when the exit of the pump is closed so that no cooling liquid flows therethrough, and Qmax represents the maximum flow rate when the exit of the pump is opened, so as to remove the pressure loss therefrom. In this graph, the relationship between the flow rate Q and the pressure P can be determined, so that the flow rate comes to be Q0 when a pipe of pressure loss P0 is connected, for example.
In the liquid cooling system according to the present invention, since the cooling liquid is circulated within the flow passage with the pulsation thereof, by use of such a reciprocating pump therein, the volume change xcex94Vp in the pump housing due to supply of the pulsation (i.e., due to the reciprocating movement) can be obtained from Q/(number of vibrations f); therefore, the relationship between the volume change xcex94Vp and the pressure P can be drawn as shown in FIG. 15. Also, since the pressure P applied on the pipe and the volume change xcex94Vs in the pipe proportional to each other, the relationship comes to be indicated by a straight line (1), for example. In this instance., at a point where the straight line (1) and the characteristic curve of the pump cross, pressure P1 and volume change xcex94V1 can be determined. In a case of forming an open loop, the volume change is determined by the pressure loss P0 of the pipe, thereby obtaining the volume change xcex94V0, however if a rigid or hard pipe having small volume change therein is used, as indicated by (1), only the volume change of xcex94V1 can be obtained, which is smaller than xcex94V0. Accordingly, the flow rate is reduced, and, therefore, the cooling performance also is reduced. On the contrary, in a case where the volume change with respect to the pressure is large, as is indicated by (1), namely, in the case of using a soft pipe, since the volume change xcex94V0 becomes large at the crossing point of the straight line (2) with the characteristic curve of the pump, the primary volume change can be obtained at xcex94V0, and, therefore, it is possible to exhibit sufficient characteristics. Thus, if the volume change due to the reciprocal movement of the pump member is represented by xcex94Vp, the pressure caused by the volume change xcex94Vp is represented by P, and the volume change of an expansible portion of the pipe when the pressure P is applied thereon is represented by xcex94Vs, it is possible to achieve those characteristics which allow the liquid cooling system to operate at high efficiency by making xcex94Vs larger than xcex94Vp, and it is also possible for the system to operate with a low electric power consumption.
Also, in a liquid cooling system comprising two pumps for pressurizing the liquid by reciprocal movement of members therein, a heat receiving jacket which functions as a heat exchanger for cooling a heat generating body, a heat radiation pipe for conducting heat exchange with the outside air, and a connector pipe for connecting these parts, the two pumps, the heat receiving jacket and the heat radiation pipe are disposed in a closed loop by means of the connector pipe, and the cooling liquid fill up the two (2) pumps, the heat receiving jacket, the heat radiation pipe, and the connector pipe. Therefore, the same effect can be obtained by shifting the phase of the reciprocal movements of the members in the two pumps by 180xc2x0. Therefore, it is possible to achieve those characteristics or performances of the liquid cooling system which allow it to operate with high efficiency, thereby to provide a system of low electric power consumption as well.